The MEN1 gene is a tumor suppressor gene identified by positional cloning by an NIH collaborative group including members of MDB. Germline mutations in the gene are found in affected subjects of MEN1 kindreds, and somatic mutations in the gene have been identified in sporadic endocrine and other tumors. The gene encodes a 610 residue protein termed menin without homology to other known proteins and without obvious functional motifs. We have initiated a series of studies aimed at defining the structure, function, subcellular localization, and range of expression of menin. We have generated a series of polyclonal peptide antisera that have proved useful in immunoblot and immunoprecipitation studies. Furthermore,these antibodies detect the expression of recombinant forms of menin to be used for structural and biochemical analyses.The cDNA encoding menin has been transiently transfected in 293 cells and antibodies used to monitor its expression after subcellular fractionation. These studies in conjunction with studies of GFP-tagged menin conducted by our collaborators in NHGRI have shown that menin is primarily localized to the nucleus. A drosophila cell expression system has been established with menin stably transfected. This has enabled us to purify menin from cultured cells using immunoaffinity chromatography. Purified menin will be used for detailed biochemical and structural studies aimed at elucidating the normal function of this tumor suppressor gene product, and clarifying how mutations in the gene cause loss of function.